Remove EUROMOD comparator facts from Belgium targets

[MaxGhenis]

Summary

• remove the JRC/EUROMOD-BE comparator source package that was included in Add Belgium target source packages #72
• remove the EUROMOD alias, comparator regression test, source artifacts, and bundle coverage rows
• keep the Belgium target set to the six primary publisher streams from Statbel/SPF Finances/ONSS/ONEM-RVA/NBB

Facts

• Belgium Ledger coverage is now 587 facts across the six primary-source streams
• EUROMOD/JRC comparator rows are excluded because Ledger facts should come from primary government/statistical publishers

Verification

• uv run pytest -q tests/test_belgium_targets.py tests/test_ledger_source_package.py
• uv run pytest -q tests/test_ledger_bundle.py::test_build_bundle_writes_merged_consumer_contract
• uv run ruff check
• git diff --check origin/main...HEAD

Refs #69

[MaxGhenis]

Closing after lead review — this PR overshoots the rule it enforces, and the rule is already enforced structurally.

The primary-source-only rule governs what may be a calibration target: model outputs must never enter the target surface. That is already guaranteed two ways: (1) every row in this package is typed entity_role: validation_comparator, which the target compiler cannot bind as a target; (2) none of the six binding Belgian ledger_selector streams (Statbel, ONSS, ONEM, SFPD, NBB, BFP — see #69) select from it.

What this PR deletes is the validation comparator itself, which issue #69's acceptance criteria explicitly require: it feeds the populace#264 EUROMOD-oracle comparison (the independent-engine agreement result). The rows record what JRC published in the 2025 Belgium country report — including the report's own external/administrative columns and ratios — with per-row source URLs and a sha256-pinned artifact. "A publisher asserted X" is a fact under this repo's charter; asserting it as a comparator is exactly the typed role the schema provides.

Merging this would also break two currently-green tests (test_belgium_euromod_comparator_has_source_urls_per_row, test_ledger_bundle.py) and the bundle counts that #82 just re-verified.

If a Belgian target profile is ever found binding a euromod-series fact, that binding — not the package — is the bug to fix.